Technical Field
[0001] The present invention relates to an alarm device attached to an electrical discharge
machine, and more particularly, to an alarm device adapted automatically to give an
alarm when the temperature of a machining fluid is off during electrical discharge
machining.
Background Art
[0002] If the temperature of a machining fluid fluctuates during electrical discharge machining,
the specific resistance of the machining fluid and hence, the machining speed, fluctuate,
and also, the dimensions of a workpiece vary. As a result, the stability of the electrical
discharge machining is ruined, and the machining accuracy is lowered. Conventionally,
therefore, when the machining fluid temperature detected by means of a temperature
sensor, such as a thermostat, exceeds an allowable upper limit value, the operation
of a cooler for cooling the machining fluid is started. When the machining fluid temperature
is lower than an allowable lower limit value, the operation of the cooler is stopped.
Thus, the machining fluid temperature is controlled within a predetermined range of
temperature.
[0003] Even in an electrical discharge machine provided with such a machining fluid temperature
control system, however, if the cooler or the temperature sensor goes wrong, or if
the electrical discharge machining is executed without connecting the cooler to the
power supply, for example, the machining fluid temperature deviates from the predetermined
temperature range, so that the aforementioned awkward situation is entailed. Namely,
the stability of the electrical discharge machining is ruined if the machining fluid
temperature rises too high, or the machining fluid is frozen if it is excessively
cooled, for example.
Disclosure of the Invention
[0004] The object of the present invention is to provide a machining fluid off-temperature
alarm device used in an electrical discharge machine and adapted automatically to
give an alarm when the machining fluid temperature is off during electrical discharge
machining.
[0005] In order to achieve the above object, according to the present invention, there is
provided a machining fluid off-temperature alarm device attached to an electrical
discharge machine, in which a machining fluid temperature adjuster is controlled so
that a detected machining fluid temperature is within an allowable temperature range,
in response to an output signal of a temperature sensor indicative of whether the
machining fluid temperature is within said allowable temperature range.
[0006] This alarm device comprises a setter for setting a predetermined temperature range
covering the allowable temperature range, a second temperature sensor provided independently
of the temperature sensor, and alarm means. The second temperature sensor detects
the machining fluid temperature, determines whether the detected machining fluid temperature
is within the predetermined temperature range, and delivers a signal indicative of
the result of the determination. The alarm means gives an alarm in response to the
output signal of the second temperature sensor, indicative of a deviation of the detected
machining fluid temperature from the predetermined temperature range.
[0007] Preferably, the machining fluid off-temperature alarm device includes halt means
for stopping the operation of the electrical discharge machine in response to the
output signal of the second temperature sensor, indicative of the deviation of the
detected machining fluid temperature from the predetermined temperature range.
[0008] According to the present invention, as described above, the alarm is given when the
machining fluid temperature deviates from the predetermined temperature range which
covers the allowable temperature range, due to some trouble in the machining fluid
temperature sensor or the machining fluid temperature adjuster, or a failure to connect
the temperature adjuster to the power supply, and preferably, the operation of the
electrical discharge machine is stopped when the alarm is given. Thus, lowering of
machining accuracy, fluctuation of machining speed, and unstable electrical discharge
machining, which are attributable to the off- state of the machining fluid temperature,
can be prevented.
Brief Description of the Drawings
[0009]
Fig. 1 is a schematic view showing the principal part of a wire-cut electrical discharge
machine furnished with a machining fluid off-temperature alarm device according to
one embodiment of the present invention; and
Fig. 2 is a diagram for illustrating the operation of the alarm device of Fig. 1.
Best Mode of Carrying Out the Invention
[0010] In Fig. 1, a wire-cut electrical discharge machine, furnished with a machining fluid
off-temperature alarm device according to one embodiment of the present invention,
comprises a machining fluid tank 1 for storing a machining fluid, a machining fluid
temperature adjuster formed of, for example, a cooler 2 communicating with the machining
fluid tank 1 and adapted to cool the machining fluid, and a numerical control device
3 including a display unit formed of, for example, a CRT display unit 6, and used
to control the operation of various parts of the electrical discharge machine. The
machining fluid tank 1 and the cooler 2 are arranged in a conventional machining fluid
circulating system (not shown) attached to the electrical discharge machine.
[0011] The electrical discharge machine further comprises first and second temperature sensors
S1 and S2, which includes first and second probes 81-1 and 81-2, respectively, for
machining fluid temperature detection located at a predetermined height position in
the machining fluid tank 2. The first temperature sensor S1 is disposed in the cooler
2, along with a first temperature setter 4 for setting the allowable range of the
machining fluid temperature, and is connected to the first temperature setter 4 and
a control unit (not shown) for controlling the operation of the cooler 2 in response
to the output of the sensor S1. The first temperature sensor S1 serves to determine
whether the actual value of the machining fluid temperature detected by means of the
probe S1-1 is within the allowable temperature range, and deliver an output signal
indicative of the result of the determination to the control unit of the cooler 2.
Further, the second temperature sensor 5, which is connected to the numerical control
device 3 and a second temperature setter 5 for setting a predetermined temperature
range covering the aforesaid allowable temperature range, serves to determine whether
the actual value of the machining fluid temperature detected by means of the probe
S2-1 is within the allowable temperature range, and deliver an output signal indicative
of the result of the determination to the numerical control device 3. These elements
3, 5, 6, S2 and S2-1 constitute the machining fluid off-temperature alarm device.
[0012] Referring now to Fig. 2, the operation of the electrical discharge machine with the
machining fluid off-temperature alarm device of the aforementioned construction will
be described.
[0013] Before the start of the operation of the electrical discharge machine, an operator
sets an allowable upper limit value T1 and an allowable lower limit value T2, which
define the allowable range of the machining fluid temperature T, in the first temperature
setter 4. Also, an upper limit value T3 greater than the value T1 by a first predetermined
value and a lower limit value T4 smaller than the value T2 by a second predetermined
value are set in the second temperature setter 5 (T4 < T2 < T1 < T3). Namely, a predetermined
temperature range defined by the values T3 and T4 and covering the allowable temperature
range is set in the second temperature setter 5. The first and second predetermined
values associated with the setting of the values T3 and T4 are determined in consideration
of a normal detection delay of the first temperature sensor S1, a normal operation
delay of the cooler 2, and the like.
[0014] After the start of the operation of the electrical discharge machine, the machining
fluid temperature T generally rises with the lapse of time. During electrical discharge
machining, the first temperature sensor S1 in normal operation compares the actual
value of the machining fluid temperature T detected by means of the probe S1-1 with
the values T1 and T2 set in the first temperature setter 4, and delivers a signal
indicative of the result of this comparison to the control unit of the cooler 2. Thus,
the output signal of the first temperature sensor Sl is on its first level when the
machining fluid temperature T is within the allowable range defined by the values
T1 and T2, and on its second level when the temperature T is off the allowable range.
Likewise, the second temperature sensor S2 compares the actual value of the machining
fluid temperature T detected by means of the probe S2-1 with the values T3 and T4
set in the second temperature setter 5, and delivers a signal indicative of the result
of this comparison to the numerical control device 3. Thus, the output signal of the
second temperature sensor S2 is on its first level when the machining fluid temperature
T is within the predetermined range defined by the values T3 and T4, and on its second
level when the temperature T is off the predetermined range.
[0015] If the machining fluid temperature T attains the allowable upper limit value T1 so
that the output signal of the first temperature sensor S1 changes from the first level
to the second level, while the first temperature sensor S1 and the cooler 2 are normally
operating, the control unit of the cooler 2 causes the cooler 2 to start operation.
As a result, the machining fluid is cooled, so that the machining fluid temperature
T lowers. Thus, as long as the detection delay of the first temperature sensor S1
and the operation delay of the cooler 2 are normal, the machining fluid temperature
T never exceeds the upper limit value T3 set in the second temperature setter 5. If
the machining fluid temperature T attains the allowable lower limit value T2 so that
the output signal of the first temperature sensor S1 changes from the second level
to the first level, thereafter, the cooler control unit stops the operation of the
cooler 2, so that the machining fluid temperature T rises. In consequence, the machining
fluid temperature T is never lower than the lower limit value T4 set in the second
temperature setter 5. Thus, when the first temperature sensor S1 and the cooler 2
are in normal operation, the cooler operation is on-off controlled in response to
the output signal of the sensor, so that the machining fluid temperature T is controlled
within the allowable range.
[0016] In case of abnormal operation of the first temperature sensor S1 or the cooler 2,
attributable to some trouble in the first temperature sensor S1 or the cooler 2 or
a failure to connect the cooler 2 to the power supply, the operation of the cooler
2 sometimes cannot be started even when the machining fluid temperature T exceeds
the allowable upper limit value T1, or the cooler operation sometimes cannot be stopped
even when the temperature T is lower than the allowable lower limit value T.
[0017] If the machining fluid temperature T exceeds the predetermined upper limit value
T3 greater than the allowable upper limit value T1, due to such an abnormal situation,
the output signal of the second temperature sensor S2 changes from the first level
to the second level. Namely, an alarm signal is delivered from the sensor S2. In response
to this alarm signal, the numerical control device 3 causes the CRT display unit 6
to display a message to the effect that the machining fluid temperature is off. Preferably,
the numerical control device 3 stops the operation of the electrical discharge machine
the moment the message is displayed. Likewise, if the machining fluid temperature
T becomes lower than the predetermined lower limit value T4 smaller than the allowable
lower limit value T2, due to the abnormal situation, an alarm signal is delivered
from the second temperature sensor S2, so that an off- state message is displayed,
and the operation of the electrical discharge machine is stopped.
[0018] The present invention is not limited to the embodiment described above, and various
modifications may be effected therein.
[0019] In the above embodiment, for example, the off- state message is displayed on the
display unit 6 controlled by the numerical control device 3 which operates in response
to the alarm signal from the second temperature sensor S2 when the machining fluid
temperature is off. Alternatively, however, the alarm signal may be supplied to a
lamp or buzzer after being amplified, without being supplied to the numerical control
device, so that an alarm is given by means of the lamp or buzzer.
[0020] In the embodiment described above, moreover, the cooler 2 is used as the machining
fluid temperature adjuster. When the electrical discharge machine is operated at a
low open-air temperature, however, a heater may be used as the machining fluid temperature
adjuster. In this case, the heater is turned on when the machining fluid temperature
T attains the allowable lower limit value T2, and is turned off when the allowable
upper limit value T1 is attained. If necessary, the electrical discharge machine may
be provided with both the cooler and the heater so that either of them can be alternatively
used.
[0021] Although the present invention is applied to the wire-cut electrical discharge machine
in the above embodiment, furthermore, it may be also applied to electrical discharge
machines of any other types.
1. In a machining fluid off-temperature alarm device attached to an electrical discharge
machine, in which a machining fluid temperature adjuster is controlled so that a detected
machining fluid temperature is within an allowable temperature range, in response
to an output signal of a temperature sensor indicative of whether the machining fluid
temperature is within said allowable temperature range, the machining fluid off-temperature
alarm device, comprising:
a setter for setting a predetermined temperature range covering said allowable temperature
range;
a second temperature sensor provided independently of said temperature sensor and
adapted to detect said machining fluid temperature, determine whether said detected
machining fluid temperature is within said predetermined temperature range, and deliver
a signal indicative of the result of said determination; and
alarm means for giving an alarm in response to the output signal of said second temperature
sensor, indicative of a deviation of said detected machining fluid temperature from
said predetermined temperature range.
2. A machining fluid off-temperature alarm device according to claim 1, further comprising
halt means for stopping the operation of said electrical discharge machine in response
to said output signal of said second temperature sensor, indicative of the deviation
of said detected machining fluid temperature from said predetermined temperature range.
3. A machining fluid off-temperature alarm device according to claim 2, wherein said
machining fluid off-temperature alarm device is attached to a wire-cut electrical
discharge machine as said electrical discharge machine.